Air handling apparatus



Jan. 2, 1951 D. D. HERRMAN AIR HANDLING APPARATUS Filed May 21, 1946 .DONA LD.D. H E RRMAN ATTORNEYS Patented Jan. 2, 19 51 AIR HANDLING APPARATUS Donald D. Herrman, Piqua, Ohio, assignor to Hartzell Industries, Inc., Piqua, Ohio, a corporationof Ohio Application May 21, 1946, Serial No. 671,360 3 Claims. (01. 230-120) This invention relates in general to air handling apparatus and particularly the means for increasing the efficiency of operation of propeller type fans.

An object of the invention is to provide an annulus or shroud for a propeller type fan having a predetermined contour for providing for a smooth acceleration of air through the shroud by the tip of the propeller operating within the shroud.

Another object of the invention is to provide an air-handling apparatus wherein a propeller type fan is rotated within an annulus or shroud with the tip of the propeller contained within the shroud, and wherein the propeller is so positioned within the shroud that the tip of the propeller is sealed against return flow of air, said sealing being occasioned by having the propeller of slightly larger diameter than the discharge orifice of the shroud by a selected and predetermined amount.

Another object of the invention is to provide an air-handling apparatus in accordance with the foregoing object wherein the efficiency of operation of the apparatus is increased through controlling the width of the shroud relative to the discharge orifice, and wherein the radius of contour of the shroud is held within predetermined limits relative to the diameter of the discharge orifice.

Still another object of the invention is to provide an air-handling apparatus in accordance with the foregoing objects wherein the shroud is provided with a rounded edge on the upstream side of the fan to provide for a gradual increase of air velocity by the tip of the fan operating within the shroud.

Further objects and advantages will become apparent from the drawings and the description.

In the drawings:

Figure 1 is a vertical cross-sectional view of an air-handling apparatus constructed in accordance with this invention.

Figure 2 is a cross-sectional view taken through the annulus or shroud to illustrate the contour of the shroud and the position of a propeller type fan therein in accordance with this invention.

' Figure 3 is a cross-sectional view of an annulus or shroud similar to Figure 2 but illustrating the invention as applied to a shroud of larger diameter than that of Figure 2.

Figure 4 is a cross-sectional view similar to 2 and 3 but illustrating the invention as applied to an annulus of still larger diameter.

It is well known in the art of air handling devices that propeller type fans rotating in open air produce considerable air agitation at the tip of. the blades of the fan Without producing any substantial delivery of air under pressure. Various types of shrouds or annulus have been tried for the purpose of increasing the efficiency of delivery from propeller type fans, particularly by the blade tips, and for increasing the pressure against which the ,fans will operate satisfactorily for efficient delivery. The efficiency of operation of a propeller type fan falls ofi rapidly as the volume of air handled by the fan destatic pressure.

It has therefore been the endeavor of personsin this art to develop a propeller type fan and shroud or annulus for the same that will maintain an'efiicient delivery of air over a greater range of air deliveries, and will maintain efficient delivery of air against greater static pressure without greatly increasing the horsepower to operate the fan.

I have found in the development of propeller type fans that the contour of the shroud or annulus in which the fan operates plays an extremely vital part in determining the efficiency of operation of a fan. Also, I have found that the position of a propeller type fan within a shroud, even of proper contour, also plays a vital part in determining the efiiciency of operation of the fan.

Primarily, the width of the annulus or shroud should be properly proportioned relative to the discharge opening of the shroud, and the radius of curvature of the shroud bears a definite relationship to the discharge orifice of the shroud.

If the shroud or annulus is properly contoured in accordance with this invention, and a propeller type fan is placed within the shroud for operation therein with the tip of the blades of the fan operating within the shroud and substantially sealed to the shroud by the close location of the tips to the shroud with the proper amount of blade overlap of the discharge orifice of the shroud, the efiiciency of operation of the air-handling device will be greatly increased and the device will be able to operate against greater static pressures without losing its eflicient air delivery.

In this invention the shroud or annulus I0 is circular in transverse cross-section. A propeller type fan H is positioned within the shroud i0 and is adapted to be driven by any suitable source of power. The blades I2 of the propeller II have '20 of the annulus i0, and is smaller than the inlet orifice I4. Also, it will be noted that the propeller tips are disposed within the annulus ill for reasons hereinafter disclosed with regard to development of efficiency in the air handling device.

The annulus ID is provided with a contoured or curved wall I that has the radius thereof generated from a plane substantially in the plane of the minimum diameter of the discharge orifice 29, which radius bears a relationship to th diameter of the discharge orifice 20 in the manner hereinafter disclosed.

The upstream edge of the wall l5, which forms the inlet orifice I4, is provided with a reversely curved position it of substantially aerofoil crosssection, thereby eliminating a sharp edge at the inlet orifice I l. The downstream side of the wall [5 is provided with a radially increasing opening which terminates in a radial flange H which thereby terminates the discharge orifice 20 with asmall radiused ccrner l8.

As previously stated the contour of the shroud wall '15 and the position of the propeller therein is extremely important to obtaining maximum efiioiency of operation of the propeller fan H With reference to Figure 2 there is illustrated the special contour of the shroud wall 55 and the position of the fan blades i2 relative thereto for obtaining maximum efiiciency of operation-of the propeller fan.

The diameter of the discharge orifice 29 is indicated by the letter O and is the basic factor from which the other dimensions of the shroud l0 areestablished and to which the other dimensions of the shroud must bear a definite relationship within predetermined limits to obtain a shroud of satisfactory contour to obtain maximum efficiency from the propeller fan.

The width of the shroud i8 is indicated by the letter W. .If the width of the shroud is too great there is undue friction to movement of air across the-surface 0f the shroud, and adjacent thereto, which detracts from the maximum emciency of air delivery by the tips of the propeller blades. On the other hand if the width of the shroud is too small there will be an insufficient surface area of the shroud for directing the air "on the upstream side of the propeller blade toward the tip of the blade in a smoothly accelerating rate,

and again the efficiency of delivery by th pro-- peller tips will be decreased. I have therefore established that the width of the shroud bears a definite relationship to the diameter of the discharge orifice, and this relationship is that the width of the shroud shall be equal to the diameter of the-orifice multiplied by .1, as a minimum dimension, and multipled by .2 as a maximum dimension. Using the letters previously referred to the equation would be W=O .l to .2. In other words the width of the shroud shall be from 10 to 20 per cent of the diameter of the discharge orifice.

-I have also found that to give the maximum efficiency to vair delivery by the tips of a propeller blade that it is essential that the shroud wall be arranged upon a curve, and that the curvature of this wall I5, to obtain maximum efficiency of air delivery by the blade tips, bears a definite relationship to the discharge orifice 2c of the shroud. In Figure 2 the radius of curvature of wall [5 is represented by the letter R, and this radius has its point of origin substantially in the plane of minimum diameter of the discharge orifice 20.

In Figure 2 it will be noted that the minimum diameter of the discharge orifice 20 is upstream from the discharge face 20A. The plane in which the'radiusiR, has its origin is this :plane of minimum'diame'terof the discharge orifice 20. Also, the point of origin of the radius R in the plane of minimum diameter of the orifice O is radially outside of the minimum diameter of the orifice -by a dimension equal to the radius R.

The radius R of the curvature of the wall l5 -ofthe-shroudhas :been established to have a definite relationship to the orifice diameter 0 multiplied by ..l to .2 as a maximum radius. Again using the letters referred to previously the equation'would be R=O .1 to .2.

The inlet opening M of the shroud I0 is provided with a rounded nose i-5 as previousy referred to, which is substantially in the form of a leading edge of an aerofoil to thereby cause the air entering the inlet on the upstream side of the shroud ii], to enter the shroud without shock and at a smoothly increasing velocity.

The downstream side of the shroud Ii] terminates in the radius corner i8 to avoid the development of air agitation and eddy currents at this point.

It has also been stated that the position of the propeller within the shroud .ID is of extreme importance, and that the diameter of the propeller, represented by the letter 5-1 in Figure -2 bears a definite relationship tothe orifice diameter 0. It is essential that the tip diameter of the propeller, that is the disc swept out by the propeller blades during rotation, be greater than the discharge diameter '0 of the discharge orifice 20 and shall be less than the inlet diameter of the shroud I0. I have determined a :definite relationship between the tip diameter T of the propeller H and the diameter 0 of the orifice 29 which obtains the maximum efficiency of air deli-very between blade tips of the propeller.

If the tip diameter of the propeller is toosmall,

even though larger than the diameterO of the discharge orifice 20, an-efiective seal is not provided .between the propeller and the wall [5 of the shroud id to prevent air currents reversing within the shroud .and vproducing air disturbance at the propeller tip which reduces the efliciency at the propeller tip in handling of air delivered through the shroud. Also, if the tip diameter of the propeller is greater than the diameter -0 of the discharge orifice '28 beyond a predetermined limit the maximum eificiency of air handling by the blade tips falls off rapidly. At 'all times, and within the :limits of tip diameters established by this invention, I have found that the propeller tips must be positioned within the shroud iii and in extremely close proximity to the wall I5.

I have found that the relationship between the tip-diameter To-f the propeller and the diameter 0 of the discharge orifice 28 shall be equal to the diameter 'Oof the discharge orifice multiplied by 1.01 as a minimum tip diameter and shall be equal to the diameter 0 multiplied by L04 as a maximum diameter. In other words the :diameter of the propeller, that is, the disc swept out by the blades in rotation thereof, relative to the diameter of the discharge orifice shall be greater by an amount 'of from one per cent to four per cent. Using the letters as previously referred to, we find the equation to be T=O 1.01 to 1.04.

In Figure 2 there is shown in full lines the position of the propeller l I relative to the shroud 0 with the tip diameter T of the propeller at the minimum diameter thereof greater than the diameter of the orifice 20. The position of the propeller ll relative to the shroud wall 15 with the tip diameter T at its maximum diameter relative to the diameter 0 of the orifice 20 is illustrated in dotted lines.

In Figure 1 there is illustrated the air flow through the tip of the propeller obtained by the use of this invention. The contoured inlet throat on the upstream side of the propeller provides for an area of relatively low pressure around the periphery thereof causing the air to greatly increase in velocity in its movement to the tip of the propeller and because of the curved inlet throat and aerofoil section on the nose of the inlet throat, the air moves toward the propeller tip, without shock, and with gradual increased velocity. The air handled by the propeller tips is completely delivered to the downstream side of the propeller because the propeller tips, working in close proximity to the wall I5, eifectively seal against reverse movement of air Within the shroud.

An air handling device constructed in accordance with this invention is capable of delivering substantially increased quantities of air against relatively high static pressures. Also, the total efilciency of the fan is maintained over a longer period on the fan curve, that is, the efficiency is maintained at a high level with greater quantities of air delivered by the fan without any substantial increase in the horse-power required to obtain the higher air deliveries, and without sacrifice of efficiency when working against higher static pressures. Thus the static efiiciency of the fan also increases. As for example, an apparatus constructed in accordance with the invention has been tested to deliver 5,000 C. F. M. at a fan efiiciency of seventy-two and one half per cent with use of .45 B. H. P.

In Figure 2 the contour of the shroud wall and the position of the propeller fan therein has been based upon an orifice diameter 0 of twentytwo inches. In Figure 3 there is illustrated the relationship between the members heretofore related to as based upon an orifice diameter 0 of thirty-six inches, and in Figure 4 the orifice diameter 0, is forty-eight inches. In each instance the shroud contour has been formulated according to the relationships heretofore set forth at the lower limits.

While the apparatus shown and described herein constitutes a preferred form of the invention, it should be understood that the apparatus is capable of alteration without departing from the spirit of the invention and that all modifications that fall within the scope of the appended claims are intended to be included herein.

Having thus fully described my invention, What I claim as new and desire to secure by Letters Patent is:

1. An air handling apparatus comprising, an

annulus having a discharge opening of less diameter than the inlet opening thereof and having an arcuate inner peripheral wall extending from the inlet opening to the outlet opening, said arcuate wall having a radius of between ten per cent and twenty per cent of the minimum diameter of the discharge opening and generated from a radial plane substantially coincident with the minimum diameter of said discharge opening, and terminating in a substantially aerofoil contour at the leading inlet edge thereof, and a propeller fan positioned in said annulus with the blade tips thereof in close proximity to the inner peripheral surface of said annulus and having a diametral overlap of the discharge opening by the disc swept out by the rotation of the blades of between one per cent and four per cent of the diameter of the discharge opening.

2. An air handling appartaus comprising, an annulus having a discharge opening of less diameter than the inlet opening thereof and having an arcuate inner peripheral wall extending from the inlet opening to the outlet opening, said arcuate wall having a radius of between ten per cent and twenty per cent of' the minimum diameter of the discharge opening and generated from a radial plane substantially coincident with the minimum diameter of said discharge opening, and a propeller fan positioned in said annulus with the blade tips thereof in close proximity to the inner peripheral surface of said annulus and having a diametral overlap of the discharge opening by the disc swept out by the rotation of the blades of between one per cent and four per cent of the diameter of the discharge opening.

3. An air handling apparatus comprising, an annulus having a discharge opening of less diameter than the inlet opening thereof and having an arcuate inner peripheral wall extending from the inlet opening to the outlet opening, said annulus having a width of between ten per cent and twenty per cent of the minimum diameter of the outlet opening, said arcuate wall having a radius of between ten per cent and twenty per cent of the minimum diameter of the discharge opening and generated from a radial plane substantially coincident'with the minimum diameter of said discharge opening, and a propeller fan positioned in said annulus with the blade tips thereof in close proximity to the inner peripheral surface of said annulus and having a diametral overlap of the discharge opening by the disc swept out by the rotation of the blades of between one per cent and four per cent of the diameter of the discharge opening.

DONALD D. HERRMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,407,889 Schmidt Feb. 28, 1922 1,427,859 Schmidt Sept. 5, 1922 1,993,158 Funk Mar. 5, 1935 2,030,375 Kort Feb. 11, 1936 

